1. Field of the Invention:
The present invention relates to fluid-actuated wellbore tools, and specifically to fluid-actuated wellbore tools which are urged between operating states by a retrievable source of pressurized fluid.
2. Description of the Prior Art:
Fluid-actuated wellbore tools are widely known and used in oil and gas operations, in all phases of drilling, completion, and production. For example, in well completions and work-overs a variety of fluid-actuated packing devices are used, including inflatable packers and bridge plugs. In a work-over operation, a fluid actuated wellbore tool may be lowered into a desired location within the oil and gas well, downward through the internal bore of wellbore tubular strings such as tubing and casing strings.
Recent advances in the technology have allowed fluid-actuated wellbore tools to be lowered into the wellbore through the production tubing on either a wireline assembly or a coiled-tubing workstring. Coiled-tubing workstrings are usually coupled to a pumping unit disposed at the surface, which provides pressure to an actuating fluid which is usually, but not necessarily, a wellbore fluid. The pump at the surface of the wellbore usually has sufficiently high levels of pressure to completely, and reliably, actuate the fluid-actuated wellbore tool.
In contrast, wireline-suspended pumps which are lowered into the wellbore are subject to stringent geometric constraints, particularly when intended for through-tubing operations, and are thus low-power devices, which are rather delicate in comparison with conventional pumps. At peak operating loads which are reached when operating at high pressures, the wireline-suspended pumps are subject to risk of failure, so it is one important objective to minimize the amount of time wireline-suspended pumps are operating at peak loads. However, it is equally important that wellbore tools are fully actuated to prevent expensive and catastrophic mechanical failures in the wellbore, such as can occur when packers and bridge plugs become unset.
Fluid-actuated wellbore tools which include elastomeric components are particularly susceptible to mechanical failure if not fully inflated. For example, fluid-actuated inflatable packing devices, such as inflatable packers and bridge plugs, include substantial elastomeric components, such as annular elastomeric sleeves, which are urged by pressurized wellbore fluids between deflated running positions and inflated setting positions. Of course, in the inflated setting position, the elastomeric components of wellbore packers and bridge plugs are essential in maintaining the wellbore tool in gripping engagement with wellbore surfaces.
Unfortunately, elastomeric sleeves have some mechanical characteristics which can present operating problems. Specifically, elastomeric sleeves require some not-insignificant amount of time to make complete transitions between deflated running positions and inflated setting positions.
It has been discovered that wellbore elastomeric sleeves require several minutes at high inflation pressures to completely conform in shape to the wellbore surface against which it is urged. This process of setting the shape of the elastomeric sleeve is known as "squaring-off" of the elastomeric element. To allow for the beneficial squaring-off of the elastomeric element, a high inflation pressure must be maintained for a brief interval of time once the packer or bridge plug is fully inflated. If the high inflation pressure is not maintained while the packer or bridge plug squares off, squaring off may occur after the inflating pressure is released resulting in a diminished gripping engagement with the casing.
When a wireline-suspended pump is employed, the objective of minimizing peak load operation of the pump is in direct opposition to the objective of maintaining a high setting pressure for a sufficient length of time to allow full and complete actuation and squaring off of the fluid-actuated wellbore tool. This conflict presents a serious operating consideration, which requires considerable judgment which is often only found in very experienced operators.
Prior art systems also include another problem which causes concern. Electric power which is supplied to the wireline-suspended pump is monitored by the operator at the surface of the oil and gas well to determine when the subsurface fluid-actuated wellbore tool is in a desired operating condition. However, the data provided by the electric power monitoring unit is difficult to interpret, and includes a fleeting, but essential, indication of changes in operating conditions of the fluid-actuated wellbore tool, which can be misinterpreted or missed altogether by a distracted, unobservant, or inexperienced operator.